Nanocluster Surface Microenvironment Modulates Electrocatalytic CO2 Reduction.

The catalytic activity and product selectivity of the electrochemical CO2 reduction reaction (eCO2RR) depend strongly on the local microenvironment of mass diffusion at the nanostructured catalyst and electrolyte interface. Achieving a molecular-level understanding of the electrocatalytic reaction requires the development of tunable metal-ligand interfacial structures with atomic precision, which is highly challenging. Here, the synthesis and molecular structure of a 25-atom silver nanocluster interfaced with an organic shell comprising 18 thiolate ligands are presented. The locally induced hydrophobicity by bulky alkyl functionality near the surface of the Ag25 cluster dramatically enhances the eCO2RR activity (CO Faradaic efficiency, FECO: 90.3%) with higher CO partial current density (jCO) in an H-cell compared to Ag25 cluster (FECO: 66.6%) with confined hydrophilicity, which modulates surface interactions with water and CO2. Remarkably, the hydrophobic Ag25 cluster exhibits jCO as high as -240 mA cm-2 with FECO >90% at -3.4 V cell potential in a gas-fed membrane electrode assembly device. Furthermore, this cluster demonstrates stable eCO2RR over 120 h. Operando surface-enhanced infrared absorption spectroscopy and theoretical simulations reveal how the ligands alter the neighboring water structure and *CO intermediates, impacting the intrinsic eCO2RR activity, which provides atomistic mechanistic insights into the crucial role of confined hydrophobicity.

Atom-Precise Heteroatom Core-Tailoring of Nanoclusters for Enhanced Solar Hydrogen Generation.

While core-shell nanomaterials are highly desirable for realizing enhanced optical and catalytic properties, their synthesis with atomic-level control is challenging. Here, the synthesis and crystal structure of [Au12 Ag32 (SePh)30 ]4- , the first example of selenolated Au-Ag core-shell nanoclusters, comprising a gold icosahedron core trapped in a silver dodecahedron, which is protected by an Ag12 (SePh)30 shell, is presented. The gold core strongly modifies the overall electronic structure and induces synergistic effects, resulting in high enhancements in the stability and near-infrared-II photoluminescence. The Au12 Ag32 and its homometal analog Ag44 , show strong interactions with oxygen vacancies of TiO2 , facilitating the interfacial charge transfer for photocatalysis. Indeed, the Au12 Ag32 /TiO2 exhibits remarkable solar H2 production (6810 µmol g-1  h-1 ), which is ≈6.2 and ≈37.8 times higher than that of Ag44 /TiO2 and TiO2 , respectively. Good stability and recyclability with minimal catalytic activity loss are additional features of Au12 Ag32 /TiO2 . The experimental and computational results reveal that the Au12 Ag32 acts as an efficient cocatalyst by possessing a favorable electronic structure that aligns well with the TiO2 bands for the enhanced separation of photoinduced charge carriers due to the relatively negatively charged Au12 core. These atomistic insights will motivate uncovering of the structure-catalytic activity relationships of other nanoclusters.

Protein-directed synthesis of NIR-emitting, tunable HgS quantum dots and their applications in metal-ion sensing.

The development of luminescent mercury sulfide quantum dots (HgS QDs) through the bio-mineralization process has remained unexplored. Herein, a simple, two-step route for the synthesis of HgS quantum dots in bovine serum albumin (BSA) is reported. The QDs are characterized by UV-vis spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, luminescence, Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), circular dichroism (CD), energy dispersive X-ray analysis (EDX), and picosecond-resolved optical spectroscopy. Formation of various sizes of QDs is observed by modifying the conditions suitably. The QDs also show tunable luminescence over the 680-800 nm spectral regions, with a quantum yield of 4-5%. The as-prepared QDs can serve as selective sensor materials for Hg(II) and Cu(II), based on selective luminescence quenching. The quenching mechanism is found to be based on Dexter energy transfer and photoinduced electron transfer for Hg(II) and Cu(II), respectively. The simple synthesis route of protein-capped HgS QDs would provide additional impetus to explore applications for these materials.